Forum Schedule Fall 2024

The potential association between the tidal disruption event (TDE) AT2019dsg and high-energy astrophysical neutrinos suggests the acceleration of cosmic rays. In addition to neutrinos, these accelerated particles could generate electromagnetic (EM) emissions spanning from radio, optical/UV, and X-ray to GeV energies through leptonic and hadronic processes. In this talk, I will present our recent results on the joint analysis of neutrino and EM cascade emissions from neutrino-coincident TDEs/candidates within an isotropic wind scenario, incorporating dust echo modeling. Moreover, I will discuss our recent work on modeling the multi-wavelength emissions from the jetted TDE AT2022cmc, where a two-component jet is considered to interpret the spectral and temporal signatures of AT2022cmc. I will demonstrate that the X-ray spectra and fast-decaying light curves extending up to 400 days post-disruption can be well explained by electron synchrotron emission from the fast jet’s reverse shock, while the radio observations could be attributed to slow jet forward shocks. A discussion of the gamma-ray and neutrino detectability of jetted TDEs will also be included.

The production mechanism of astrophysical high-energy neutrinos is not yet understood. The first astrophysical high-energy neutrino source candidate identified by IceCube at a significance level of >3sigma was a blazar, TXS 0506+056, an accreting supermassive black hole that drives a relativistic jet directed towards Earth. Recently, IceCube also discovered strong evidence that Seyfert galaxies also emit neutrinos, which appears unrelated to jet activity. In our previous works we found that gamma-ray suppression, a necessary consequence of the effective neutrino production process, results in observable dips in the gamma-ray light curve of the transient neutrino point sources. In my talk I will show that the 0.3-100 TeV neutrino - 15-55 keV unabsorbed hard X-ray flux ratio of blazars TXS 0506+056 and GB6 J1542+6129 is consistent with neutrino production in a gamma-obscured region near the central supermassive black hole, with the hard X-ray flux corresponding to reprocessed gamma-ray emission with comparable flux to that of neutrinos. Similar neutrino-hard X-ray flux ratios were found for four of IceCube’s Seyfert galaxies, raising the possibility of a common neutrino production mechanism.

Gravitational-wave (GW) astronomy has opened up a whole new window to observe the Universe. Since its first detection by the Laser Interferometer Gravitational-wave Observatory (LIGO) in 2015, a network of ground-based GW detectors detected 90 signals from compact binary mergers by 2020. In this talk, I will give an overview of the GW observations in the context of the ground-based detectors, including the recent results from the ongoing fourth observing run. In particular, I will introduce some developments I have contributed to GW detection pipeline, called GstLAL, for compact binary mergers as well as a search for stochastic GW background. Also, I briefly describe future prospects of new discoveries in the GW observation and how to improve its synergy with other means of astronomy, e.g., electromagnetic waves, in the current multi-messenger era.

Neutron star mergers, i.e., binary neutron star (BNS) and neutron star-black hole mergers (NSBH), are ideal astrophysical events that produce multi-messenger signals, including gravitational waves (GWs), and electromagnetic (EM) radiation. Detecting these signals by mutlimessenger observations provides crucial insights into the nature of these events and their role in the universe. As GW detection enters the fourth observing run, an increasing number of NS mergers, particularly NSBH mergers, have been detected by the LIGO-Virgo-KAGRA collaboration. However, we have not observed any EM counterparts to these events as expected, unlike the multimessenger observations of GW170817/GRB170817A/AT2017gfo. How can we explain this absence?

In this talk, I will discuss the reasons behind the lack of EM counterparts to NSBH mergers detected by LIGO-Virgo-KAGRA during O3 and O4, as well as the implications for future multimessenger searches of NS mergers. Additionally, I will introduce the potential EM signals from NS mergers in AGN accretion disks and their detection.

In their seminal paper, Born and Oppenheimer [1] proposed the celebrated adiabatic approximation for the separation of electronic and nuclear motions in molecules, viz., the Born-Oppenheimer Approximation, which is a cornerstone of molecular physics and the basis of most quantum chemistry calculations of molecular structure. Huang [2] later laid the foundation for the complementary diabatic approximation that can be a fruitful alternative for some computation purposes. Nevertheless, nonadiabatic interactions are ubiquitous and play important roles in molecular spectroscopy, chemical kinetics, and AMO physics. In particular, vibronic interactions couple the motion of electrons and the vibrational motion of nuclei and, hence introduce such intriguing and sometimes bewildering intramolecular dynamics as Renner-Teller, Jahn-Teller, and pseudo-Jahn-Teller effects. In my talk, I will use several exemplary molecules from my own research to demonstrate how vibronic interactions can distort geometries and potential energy surfaces of molecules, lower their symmetry, shift and/or split energy levels, and introduce transitions that would otherwise be forbidden. The molecules that I will discuss include: H2 – a homonuclear diatomic, CaOCH3 – a “pseudo” linear triatomic, CH3O – a symmetric polyatomic, and cyclohexoxy – an asymmetric polyatomic. When electron spin and molecular rotation are taken into account, the energy level structure and observable spectra of molecules with vibronic interactions are further complicated by rotational and spin interactions. Although all these complications render analyzing and understanding experimentally observed spectra more challenging, they also provide more abundant and more revealing information about molecules, which may be utilized for controlling and manipulating molecules and preparing molecules in single quantum states. Especially, “parity”-related energy levels may be used for detecting P, T-symmetry-violating interactions, and for quantum computing.[3] In this sense, vibronic interactions are both friends and foes to molecular spectroscopists and AMO physicists.

[1] “Zur Quantentheorie der Molekeln”. Born, M.; Oppenheimer, R., Ann. Phys. 389, 457-484 (1927). Translation
[2] Born, M.; Huang, K., Dynamical Theory of Crystal Lattices. 1954, Oxford: Oxford University Press.
[3] B. "Direct Laser Cooling of Polyatomic Molecules," Adv. At. Mol. Opt. Phy. 72, 89-182 (2023). See also: https://arxiv.org/abs/2302.10161

SPHEREx, NASA's next MIDEX mission, will launch in early 2025 and map the entire sky in 102 near-infrared spectral channels from 0.75-5 microns. This rich dataset will be used for a wide variety of science, including studies of objects in our own solar system, an inventory of water and CO2 ice in the Milky Way, and constraints on cosmic inflation and the structure of the Universe on the largest scales. Due to its orbit and scan strategy, SPHEREx will also naturally build up deep fields in the ecliptic poles, which will enable unprecedented studies of the extragalactic background light (EBL). The EBL encodes the history of galaxy formation stretching from today all the way into the Epoch of Reionization, over 13 Gyr ago. In this talk, I will provide an overview of SPHEREx, including its three core science themes (ices, inflation, and EBL) and the kinds of public data products it will provide. I will close with a deep dive on the EBL, the status of our team's analysis pipeline, and what we hope to learn about galaxies near and far in the next few years.

The Advanced Sources and Detectors (ASD) project is building the world’s most advanced linear induction accelerator (LIA) at the Nevada National Security Sites (NNSS). A large-scale collaboration between several national laboratories, this radiographic accelerator, known as Scorpius, will assist with answering questions about the United States’ aging nuclear stockpile. Aspects of LIA research ranging from simulations and modeling to diagnostic development are being pursued at the NNSS to build the expertise required to operate, maintain, optimize, and upgrade Scorpius. This major focus on accelerator science is in addition to ongoing fundamental and applied research in diagnostic systems, plasma devices, neutron generation, and more currently underway at the NNSS.

This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy, and the National Nuclear Security Administration. DOE/NV/03624--2051.

Quasars are among the most luminous objects in the universe. These very energetic regions lie at the center of massive galaxies and are powered by a supermassive black hole. While it has been found that there is a correlation between the mass of these supermassive black holes and the mass of the surrounding galaxies, the co-evolution of galaxies and quasars is barely understood. Outflows launched from the vicinity of supermassive black holes are a key piece in this puzzle, potentially linking the small and the large-scale phenomena.

My research group has discovered gas that is outflowing at extremely high speeds (speeds higher than 10% the speed of light!). I will present the latest survey of these now called extremely high velocity outflows observed as broad absorption lines in Sloan Digital Sky Survey Data. While this realm of the parameter space of quasar outflows has not been previously studied, it might pose the biggest constraints for theoretical models. Moreover, the energy outflows at ~0.2c carry out may reach two orders of magnitude larger than those speeding at high velocities (~10,000 km/s). Studying extremely high velocity outflows can help us understand the interaction between the central supermassive black hole and the host galaxy, so I will discuss the properties of the quasars in the found sample, as well as the current and future studies our research group is carrying out to understand what is powering these outflows and how they might evolve and affect galaxy evolution.

Within the past decade, significant progress has been made in using quantum computing (QC) for solving classical problems. In this talk, an overview is made of the ways by which QC has shown promise in turbulence and combustion research. This is via both quantum-ready and quantum-inspired algorithms. The former deals with problems that either have the potentials to benefit from quantum speed-up on universal gate-based digital computers, or those that can be solved on quantum simulators. The latter deals with new classical algorithms that have emerged from many-body quantum physics. Some recent results will be presented in which QC has proven effective for Reynolds-averaged simulation (RANS), large eddy simulation (LES) and direct numerical simulation (DNS) of turbulent flows under both non-reactive and reactive conditions.

Dr. Peyman Givi is Distinguished Professor and James T. MacLeod Chair of Mechanical Engineering and Petroleum Engineering at the University of Pittsburgh. He received Ph.D. from the Carnegie Mellon University (PA), and BE from the Youngstown State University (OH). Peyman serves on the Editorial Boards of the AIAA Journal, Combustion Theory and Modelling, and Journal of Applied Fluid Mechanics

In 1982 Blandford and Payne predicted that magnetic fields are fundamental for accretion onto supermassive black holes (SMBHs). Magnetic field lines anchored in the disk accelerate a wind via the centrifugal force, allowing for the angular momentum to be transferred out of the system and gas to accrete onto the central compact object. The wind can form a few Schwarzschild radii from the SMBH up to the nuclear torus. Almost a half century later, the detailed mechanisms of SMBH growth are still a passionate area of research. Astronomers currently debate whether winds are fuelled by jets, mechanical winds, or radiation, with magnetic processes being the least accepted explanation. In this talk, I present detailed ALMA observations of the most compact and opaque galactic nuclei in the universe, appropriately named compact obscure nuclei (CONs). CONs represent a significant phase of galactic nuclear growth, with opaque and compact centers (r < 100 pc), that conceal growing SMBHs. The analysis of these observations reveal magnetically driven molecular winds and abundances of complex organic molecules rivaling SGR b2 and Galactic hot cores. These results imply that growth of SMBHs is very similar to the growth of hot cores or protostars.